The present invention relates generally to the field of actuators for use in injection molding machines, and, more particularly, to an improved single motor-driven injection-and-screw drive hybrid actuator for an injection molding machine, or the like.
In the past, plastic injection molding machines have utilized hydraulic actuators, powered from a central hydraulic pumping system, to perform various machine functions, such as closing and holding the mold platen, rotating the plasticizer screw, and injecting the melted plastic into the mold. See, e.g., Technical Bulletin 145, xe2x80x9cControls for Injection Molding of Thermoplasticsxe2x80x9d, Moog Inc., East Aurora, New York (Jun. 1980), the aggregate disclosure of which is hereby incorporated by reference.
There is now a trend to perform these functions with a multiplicity of directly-acting electric motors. However, experience has shown that such motors are often not well matched to the load demands, and that a better solution is the use of hybrid electric/hydraulic drives, such as those shown in Japanese Utility Model Post-Examination Publication No. 3-3389, and Applicant""s pending application Ser. No. 09/709,904, both of which show hybrid mechanisms for operating mold closures. The first utilizes operation of an electric motor and screw mechanism to not only perform the primary function, but also to move a piston to compress a fluid into a hydraulic accumulator. This stored pressurized fluid is then employed subsequently to power a secondary function.
In one application, the present invention discloses a novel hybrid mechanism that stores some of the energy from the output of an electric motor that rotates the plasticizer screw of an injection molding machine. The axial reciprocating motion of the screw, which is utilized to store and inject melted plastic into the mold, is connected to a piston actuator. A pump, attached to the rotating motor shaft, is connected to the actuator so as to pump hydraulic fluid from the contracting actuator chamber when the screw is retracted, and to transfer it at high pressure into a pneumatically-charged accumulator. When the screw is to be extended, this pressurized fluid is subsequently allowed to flow back into the actuator through a metering valve that controls the rate of injection of the melted plastic into the mold.
With parenthetical reference to the corresponding parts, portions or surfaces of the disclosed embodiment, merely for purposes of illustration and not by way of limitation, the present invention broadly provides an improved device (10) for moving a load (11) rotationally and/or axially relative to a body (12).
The improved device broadly comprises: a body; a motor (13) mounted on the body and having an output shaft (14) operatively arranged to move the load rotationally relative to the body; a piston (16) movably mounted on the body and defining therewith a variable-volume first chamber (19), the piston being operatively arranged to move the load axially relative to the body; an accumulator (23) charged to a predetermined pressure; a fluid (e.g., hydraulic fluid) in the first chamber and accumulator; a pump (26) driven by the motor, the pump being operatively arranged to displace fluid from the first chamber to the accumulator; and a valve (28) operatively arranged to selectively permit pressurized fluid in the accumulator to flow into the first chamber to move the piston and load in one direction axially relative to the body, as when the load is to be extended.
In the preferred embodiment, the motor is electric, and the piston and pump are mounted coaxially with the motor output shaft. The fluid may be hydraulic fluid, and there may be a splined connection between the piston and motor output shaft. This splined connection couples the piston and load to rotate with the motor output shaft, but allows axial movement between the piston and load relative to the output shaft.
The invention may further include a variable-volume second chamber (20) defined by the piston and body. The volumes of the first and second chambers vary inversely when the piston moves relative to the body. The volumetic displacement of the first chamber may be substantially greater than that of the second chamber when the piston moves relative to the body, with the difference therebetween flowing to, or from, the accumulator. The second chamber may communicate with the fluid in the accumulator through the valve so as to selectively urge the piston to move in the opposite direction relative to the body. The valve may be an electrohydraulic servovalve, and the load may be the screw of an injection molding machine.
Accordingly, the general object of the invention is to provide an improved device for moving a load rotationally and/or axially relative to a body.
Another object is to provide an improved device for moving the screw of an injection molding machine rotationally and/or axially relative to a body.
These and other objects and advantages will become apparent from the foregoing and ongoing written specification, the drawings, and the appended claims.